processor_sql: Ensure jemalloc compiling before starting to build sql parser

[cosmo0920]

flb_mem.h wants to depend on jemalloc when FLB_JEMALLOC is turned on.
jemalloc building order itself is mostly controlled by target_link_libraries(fluent-bit-static libjemalloc). However, processor-sql-parser library does not have such dependency indication of jemalloc.
This should be lack of information for building order after the bundled jemalloc is built.
This PR fixes the order glitch.

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[edsiper]

thank you